Methods and apparatus for curing composite nacelle structure

ABSTRACT

Methods and apparatus for curing curved cylinder-like workpieces (e.g., in the shape of a half or full barrel) made of composite material, such as nacelle honeycomb core composite sandwich structures. These methods enable tailored curing of composite nacelle structures, to significantly reduce capital cost and fabrication cycle time. In lieu of an autoclave or oven, a pressurized ring-shaped cure volume is defined by a partitioned enclosure that mimics the cylinder-like shape of the composite nacelle structure with only limited clearance (e.g., a partitioned enclosure comprising inner and outer concentric cylinder-like walls). A tool (e.g., a mandrel) and at least one composite nacelle structure supported thereon are placed in the cure volume for curing. Integrally heated tooling, optionally in combination with other heating methods, such as infrared heaters, is utilized to provide the temperature profile necessary for cure.

BACKGROUND

This disclosure generally relates to methods and apparatus forfabricating composite structures. In particular, this disclosure relatesto methods and apparatus for curing composite structures, such ashoneycomb sandwich composite structures.

Airplane manufacturers are under increasing pressure to producelightweight, strong, and durable aircraft at the lowest cost formanufacture and life-cycle maintenance. An airplane must have sufficientstructural strength to withstand stresses during flight, while being aslight as possible to maximize the performance of the airplane. Toaddress these concerns, aircraft manufacturers have increasingly usedfiber-reinforced resin matrix composites.

These composites provide improved strength, fatigue resistance,stiffness, and strength-to-weight ratio by incorporating strong, stiff,carbon fibers into a softer, more ductile resin matrix. The resin matrixmaterial transmits forces to the fibers and provides ductility andtoughness, while the fibers carry most of the applied force.Unidirectional continuous fibers can produce anisotropic properties,while woven fabrics produce quasi-isotropic properties. Honeycomb coreis often sandwiched between composite sheets to provide stiff panelshaving the highest specific strength. More specifically, honeycomb coresandwich panels or composite structures, which typically comprisecomposite laminate skins co-cured with adhesives to the honeycomb core,are widely used in aerospace applications, among others, because oftheir high stiffness-to-weight (i.e., “specific stiffness”) andstrength-to-weight (i.e., “specific strength”) ratios.

Honeycomb sandwich composite structures may be fabricated utilizingvarious composite forming methods. The most commonly employed techniqueinvolves the use of a vacuum bag molding assembly wherein an imperviousmembrane or “vacuum bag” is employed for consolidating the compositeskins or layers and ensuring proper adhesion thereof to the centrallydisposed honeycomb core. More specifically, the lower or base compositeskin, the honeycomb core, and the upper or face composite skin aresequentially laid in a rigid mold member so that the honeycomb core isoverlaid or covered by the upper and lower composite skins. The upperand lower composite skins are typically formed from uncured “prepreg” or“B-stage” laminates that comprises a fiber reinforcement such asgraphite, aramid, or fiberglass fibers (e.g., linear, weaves, or both)disposed in a binding polymeric matrix such as epoxy, phenolic, or othersimilar organic resinous material. Film adhesive typically forms thebonds between the upper and lower composite skins and the honeycombcore. A vacuum bag is disposed over the rigid mold member and sealsthereto, thereby forming a mold cavity that is occupied by theuncured/unbonded composite lay-up. The mold cavity is then evacuated tosubatmospheric pressure within the mold, and superatmospheric pressureis applied to the exterior (in an autoclave), and the temperature of thecomposite lay-up is increased while in the autoclave to cure the lay-up.The combination of subatmospheric internal pressure and superatmosphericexternal pressure consolidate the composite skins, remove air andvolatiles from the resin binder, and apply the necessary compactionpressure to ensure full and uniform adhesion of the lay-up.

Because of the noise regulations governing commercial transportaircraft, high bypass engines incorporate acoustic panels within thenacelles. Conventionally, these elements are made with an innerperforated skin, a surrounding buried septum honeycomb core, and anon-perforated outer skin.

Curing of complex composite nacelle structures traditionally requires anautoclave to provide the temperature and pressure necessary for cure.Due to the high capital cost, autoclaves are typically sized to curemultiple parts in a batch, and the cost of purchase and operation ishigh due to the volume. Other methods of manufacturing, such as resininfusion, have been successfully used to eliminate the need for anautoclave or oven. However, nacelle honeycomb core composite structures,including nacelle acoustic structures in their current architecture,cannot be readily manufactured using other methods.

Improvements in methods for curing nacelle honeycomb core compositesandwich structures that reduce costs and increase production rates arewanted.

SUMMARY

The subject matter disclosed herein is directed to methods and apparatusfor curing curved cylinder-like workpieces (e.g., in the shape of a halfor full barrel) made of composite material, such as nacelle honeycombcore composite sandwich structures. The methods disclosed herein enabletailored curing of curved cylinder-like workpieces, such as compositenacelle structures, to significantly reduce capital cost and fabricationcycle time. These methods take advantage of the cylinder-like (e.g., thediameter may vary in an axial direction) geometry associated withnacelle components.

In lieu of an autoclave or oven, a pressurized ring-shaped cure volumeis defined by a partitioned enclosure that mimics the cylinder-likeshape of the uncured composite nacelle structure with only limitedclearance (e.g., a partitioned enclosure comprising inner and outerconcentric cylinder-like walls). In accordance with some embodiments,the top and bottom of the enclosure volume are defined by a fixed bottomplate and a movable top plate; the top plate is attached or connected toa pair of concentric cylinder-like walls; and a tool (e.g., a mandrel)and one or more composite nacelle structures supported thereon aredisposed in the ring-shaped cure volume for curing. Integrally heatedtooling, optionally in combination with other heating methods, such asinfrared heaters, is utilized to provide the temperature profilenecessary for curing the uncured composite nacelle structure. No changesin part configuration or materials are required, so the architecture ofnacelle acoustic structures and weight efficiency of honeycomb coresandwich structure can be preserved.

The methods and apparatus disclosed in detail hereinafter eliminate theneed for a typical autoclave but retain the ability to use equivalenttemperature and pressure for adequate cure, and significantly reduce thecure system cost. Furthermore, the mode(s) of heat transfer used in themethods disclosed in detail below enable more rapid and uniform heating.This reduces cure cycle time and energy consumption, and ensuressuperior part cure quality. Finally, the methods and apparatus disclosedherein provide an approach to composite part cure that is “right-sized”to the part and thus supports lean manufacturing objectives.

One aspect of the subject matter disclosed in detail below is anapparatus for curing a composite structure, comprising: an enclosurecomprising a top plate, a base, and an outer wall disposed between thetop plate and the base, the outer wall having a closed contour; an innerwall disposed between the top plate and the base and surrounded by theouter wall, the inner wall having a closed contour, wherein surfaces ofthe inner and outer walls, the top plate, and the base define aring-shaped cure volume; and a hollow tool comprising a surface having aclosed contour and heating elements, wherein the hollow tool surroundsthe inner wall, is surrounded by the outer wall, and is thermallycoupled to the composite structure to allow heat transfer from theheating elements to the composite structure. In accordance with someembodiments, the heating elements transform electric current into heat.In accordance with other embodiments, the heating elements carry heatedfluid. The apparatus may further comprise a heater attached to an outersurface of the inner wall and/or a heater attached to an inner surfaceof the outer wall.

Another aspect of the subject matter disclosed herein is a method forcuring a composite structure, comprising: (a) forming a tool-compositestructure assembly by placing an uncured composite structure in contactwith a surface of a tool having a closed contour and having integratedheating elements; (b) placing the tool-composite structure assembly on abase; (c) enclosing a ring-shaped cure volume having an outer boundarythat surrounds the tool; (d) activating the integrated heating elementsto heat the uncured composite structure during a cure cycle; and (e)producing a specified pressure inside the ring-shaped cure volume duringthe cure cycle. The method may further comprise: removing thetool-composite structure assembly from the ring-shaped cure volume; anddemolding the composite structure from the tool. In accordance with someembodiments, the uncured composite structure has a closed contour,surrounds the tool and is surrounded by the outer boundary of thering-shaped cure volume. The method further comprises coupling theheating elements integrated in the tool to a source of energy after step(b) and prior to step (d).

A further aspect of the subject matter disclosed herein is an apparatusfor curing a composite structure, comprising: an enclosure comprising atop plate, a base, and a wall disposed between the top plate and thebase, the wall having a closed contour; a tool disposed between the topplate and the base and surrounded by the wall, the tool comprising asurface having a closed contour and heating elements, wherein thesurface of the tool and respective surfaces of the wall and the topplate at least partly define a ring-shaped cure volume, and the tool isthermally coupled to the composite structure to allow heat transfer fromthe heating elements to the composite structure. In accordance with someembodiments, the cure volume is further partly defined by a surface ofthe base. This apparatus may further comprise means for coupling theheating elements in the tool to a source of energy and a heater attachedto an inner surface of the wall. In accordance with some embodiments,the heating elements transform electric current into heat and the sourceof energy is a current generator electrically coupled to the heatingelements. In accordance with other embodiments, the heating elementscarry heated fluid and the source of energy is a source of heated fluid.

Yet another aspect is a system comprising: an enclosure comprising a topplate, a base, and an outer wall disposed between the top plate and thebase, the outer wall having a closed contour that forms an outerboundary of an internal volume of the enclosure; a means forpartitioning the internal volume of the enclosure to form a ring-shapedcure volume disposed between the wall and the partitioning means; anuncured composite structure disposed within the cure volume; heatingelements situated to heat the uncured composite structure during a curecycle; and means for producing a specified pressure inside the curevolume during the cure cycle. In accordance with some embodiments, themeans for partitioning comprises a tool comprising a surface having aclosed contour, the heating elements being integrated in the tool, andthe tool being surrounded by the outer wall and thermally coupled to theuncured composite structure to allow heat transfer from the heatingelements to the uncured composite structure. In accordance with otherembodiments, the means for partitioning comprises an inner wall, theapparatus further comprising a hollow tool comprising a surface having aclosed contour, the heating elements being integrated in the hollowtool, wherein the hollow tool surrounds the inner wall, is surrounded bythe outer wall, and is thermally coupled to the uncured compositestructure to allow heat transfer from the heating elements to theuncured composite structure.

Other aspects of methods and apparatus for curing composite nacellestructures are disclosed and claimed below.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram representing an isometric view showing the geometryof some components of an assembled apparatus for curing a compositenacelle structure in accordance with some embodiments. The assembledapparatus is shown with a top plate of an enclosure removed.

FIG. 2 is a diagram representing a sectional view of some components ofan assembled apparatus for curing a composite nacelle structure inaccordance with one embodiment.

FIG. 3A is a diagram representing a sectional view of a portion of asealed interface between an annular recess in a base and a bottom edgeof a plug in accordance with one embodiment.

FIG. 3B is a diagram representing a sectional view of a portion of asealed interface (indicated by a dashed circle in FIG. 2) between a baseand a bottom edge of a plug in accordance with another embodiment.

FIG. 4 is a diagram representing a sectional view of a portion of anassembled part curing enclosure containing a tool-mounted part to becured (the depicted portions being indicated by a dashed circle in FIG.2) in accordance with one embodiment.

FIG. 5 is a diagram representing a sectional view of some components ofan assembled apparatus for curing a composite nacelle structure inaccordance with a plug-less embodiment.

FIG. 6 is a block diagram showing some components and subsystems of asystem for assembling the apparatus depicted in FIG. 2 or 5.

FIG. 7 is a block diagram showing some subsystems of a system for curinga composite nacelle structure in accordance with various embodiments.

FIG. 8 is a flow diagram of an aircraft production and servicemethodology.

FIG. 9 is a block diagram showing systems of an aircraft.

Reference will hereinafter be made to the drawings in which similarelements in different drawings bear the same reference numerals.

DETAILED DESCRIPTION

Various embodiments of an apparatus having a ring-shaped cure volume forcuring cylinder-like composite structures, such as composite nacellestructures, wrapped around the surface of a tool will now be describedin detail for purposes of illustration only. The apparatus comprises anenclosure that defines a ring-shaped cure volume in which the uncuredcomposite structure is disposed. In accordance with the embodiment shownin FIGS. 1, 2 and 4 (described in detail below), the inner and outerboundaries of the ring-shaped cure volume are respectively formed byinner and outer walls (also referred to herein as “plug” and “sleeve”respectively) which extend from a top plate to a base. The uncuredcomposite structure is supported by and in contact with a surface of atool having a closed contour, which tool is disposed within thering-shaped cure volume. In accordance with another embodiment, the toolthat supports the uncured composite structure forms the inner boundaryof the ring-shaped cure volume, as will be described in detail belowwith reference to FIG. 5.

A first illustrative geometry of an apparatus for curing a compositestructure 22 is schematically depicted in FIGS. 1 and 2. FIG. 1represents an overall isometric view of components of the apparatus witha top plate omitted, while FIG. 2 represents a sectional view of anapparatus including a top plate 14. In this example, an uncuredcylinder-like composite structure 22 is completely wrapped around andsupported by a tool 20, which may take the form of a hollow mandrel madeof metal or composite material. The resulting tool-composite structureassembly is disposed between a plug 18 and a sleeve 16, which (as bestseen in FIG. 1) may comprise concentric circular cylindrical inner andouter walls respectively.

Preferably, the profile of tool 20 is a closed contour. The tool 20 (ortools) can be a closed volume or may be segmented and still work. Theexternal surface of tool 20 may be shaped to conform to the inner moldline of the composite structure 22. If the inner mold line of thecomposite structure 22 is axially symmetric, then the external surfaceof tool 20 will approximate a surface of revolution. Examples ofsurfaces of revolution generated by a straight line are cylindrical andconical surfaces, depending on whether or not the line is parallel tothe axis. Surfaces of revolution generated by a curved line have aradius that varies along the axis. If the inner mold line of thecomposite structure 22 is not axially symmetric, then the externalsurface of tool 20 will not approximate a surface of revolution.

As shown in FIG. 2, the upper ends of plug 18 and sleeve 16 are attachedor connected to the top plate 14, while the lower ends of plug 18 andsleeve 16 are seated on a base 12, which may comprise a circular plate.Respective surfaces of base 12, top plate 14, and sleeve 16 form anenclosure 10 having an internal volume which is partitioned to form aring-shaped cure volume 8. In this embodiment, the internal volume ofthe enclosure 10 is partitioned by plug 18, which forms the radiallyinner boundary of the ring-shaped cure volume 8, while sleeve 16 formsthe radially outer boundary of the ring-shaped cure volume 8. Theassembly comprising tool 20 and composite structure 22 is disposedwithin the ring-shaped cure volume 8. System interfaces for providingelectrical power and for controlling the pressure inside the ring-shapedcure volume 8 may be incorporated in top plate 14 or base 12. Inaddition, equipment for monitoring the temperature and pressure insidethe ring-shaped cure volume 8 may be incorporated in top plate 14 orbase 12.

Although not shown in FIGS. 1 and 2, the tool 20 has a multiplicity ofheating elements integrated therein (see, e.g., heating elements 52 inFIG. 7). These heating elements may be distributed around the entirecircumference of tool 20 and are thermally coupled to the compositestructure 22 via the tool surface (which is in contact with thecomposite structure 22) to allow conduction and/or radiation of heatfrom the heating elements into the composite structure 22. In accordancewith some embodiments, the heating elements are resistive heatingelements, embedded in tool 20, which transform electric current intoheat. In accordance with other embodiments, the heating elementsembedded in tool 20 are pipes, tubes or capillaries which carry heatedfluid (e.g., superheated steam or hot oil).

The apparatus further comprises means for coupling the heating elementsin tool 20 to a source of energy (not shown in FIG. 2). In the exampleshown in FIG. 2, the tool 20 is seated on a circular manifold 24, whichmanifold 24 in turn is attached or connected to the base 12 and coupledto provide heating. The manifold 24 is disposed between sleeve 16 andplug 18. In cases where resistive heating elements are used, themanifold 24 may comprise electrical conductors and switches forproviding electrical current from a current generator to the resistiveheating elements. In cases where the heating elements convey heatedfluid, the manifold 24 may comprise pipes, tubes or channelsincorporated in tool 20 for distributing heated fluid current from asource of heated fluid to the distribution network inside the manifold24.

The apparatus shown in FIGS. 1 and 2 is suitable for curing compositenacelle structures. Given the generally cylindrical shape of compositenacelle structures, it is assumed for the purpose of illustration onlythat tool 20 and composite structure 22 are surfaces of revolution.However, it should be appreciated that, in the alternative, tool 20 andcomposite structure 22 do not need to be surfaces of revolution. Inaddition, as explained in detail below, the composite structure need nothave a closed contour. To simplify the discussion, it is also assumedherein that sleeve 16 and plug 18 are circular cylindrical. However, itshould be appreciated that, in the alternative, sleeve 16 and plug 18 donot need to be circular or cylindrical.

The composite structure 22 depicted in FIGS. 1 and 2 may comprise anyone of the following typical nacelle composite structures:

(a) an inlet inner acoustic panel in one 360-degree structure or in aplurality of segments, depending on the design;

(b) a fan cowl panel, typically in two segments of approximately 160degrees each;

(c) a thrust reverser outer acoustic panel, typically in two segments ofapproximately 160 degrees each;

(d) a thrust reverser outer cowl panel, typically in two segments ofapproximately 160 degrees each; or

(e) a thrust reverser inner wall panel (which, although not completelycylindrical, could conceivably be cured using the apparatus disclosedherein).

Still referring to FIGS. 1 and 2, the tool 20 may take the form of abond assembly jig that is used as the layup and cure mandrel for thecomposite structure. The tool 20 can be designed to be integrally heatedusing known methods (e.g., electrical heating elements, fluid heating,etc.). The tool 20 is preferably indexed to the base 12, for example,using mechanical guides and pins in a well-known manner. The tool 20 mayalso be designed to allow de-molding of the composite structure 22 asrequired using existing tool design approaches.

The base 12 depicted in FIGS. 1 and 2 is the platform on which the tool20 rests during a curing operation. As depicted in FIG. 4, the base 12also have provisions 50 for connecting the manifold 24 to the energysource (e.g., electrical supply or heated fluid source). In addition,the sleeve 16 and plug 18 could be fitted with suitable heaters in asuitable pattern around their circumferences to provide uniform heating.FIG. 4 shows one heater 30 attached to an outer surface of plug 18 andanother heater 32 attached to an inner surface of sleeve 16. Similarheaters can be placed around the respective circumferences of sleeve 16and plug 18.

Referring again to FIG. 2, the sleeve 16 forms the outer boundary ofring-shaped cure volume 8. Sleeve 16 is designed to withstand curepressure and sized diametrically to minimize the cure volume. The top ofsleeve 16 may be attached or connected to the top plate 14 so that thesleeve 16 is raised or lowered when the top plate 14 is raised orlowered. The bottom of sleeve 16 can be sealed against the base 12 bymeans of a typical high-temperature pressure seal. The sleeve 16 shouldbe designed to minimize heat loss during the cure cycle and may beprovided with additional heating elements.

The plug 18 forms the inner boundary of the ring-shaped cure volume 8.Plug 18 is also designed to withstand cure pressure and sizeddiametrically to minimize the cure volume. The top of plug 18 may beattached or connected to the top plate 14 so that the plug 18 is alsoraised or lowered when the top plate 14 is raised or lowered. The bottomof plug 18 can also be sealed against the base 12 by means of a typicalhigh-temperature pressure seal. The plug 18 should also be designed tominimize heat loss during the cure cycle and may be provided withadditional heating elements. The plug 18 would not be required if it isacceptable for the entire cylindrical volume to be the cure volume,based on impact to the equipment and cure cycle.

FIGS. 3A and 3B are detailed views taken from FIG. 2 that showrespective interfaces between base 12 and the bottom of plug 18 inaccordance with respective implementations.

In the implementation depicted in FIG. 3B, the plug-base interface is aplanar interface comprising a seal 28 (e.g., an O-ring with opposingseal grooves formed in the surface of base 12 and the end face of plug18). The bottom of the sleeve 16 can be sealed to the base 12 in asimilar manner.

In the implementation depicted in FIG. 3A, the interface is a recessedinterface comprising a seal 28. This recessed interface comprises arecess 26 formed in base 12 which receives the bottom of plug 18, eitherwith or without draft (e.g., beveling) on the base surface to facilitateinsertion. This recessed interface could be designed to react curepressure loads. The bottom of the sleeve 16 can be sealed to the base 12in a similar manner.

FIG. 5 is a diagram representing a sectional view of some components ofan assembled apparatus for curing a cylinder-like composite nacellestructure in accordance with an alternative embodiment which does notuse a plug. In accordance with this concept, a portion of a tool 34forms the inner boundary of the ring-shaped cure volume 8 and the plugis eliminated. The tool 36 has heating elements (of the types previouslydescribed) integrated therein and should be designed to withstand thecure pressure. The tool 34 is thermally coupled to the composite nacellestructure 22 to allow conduction and/or radiation of heat from theheating elements to the composite nacelle structure 22.

In accordance with the implementation depicted in FIG. 5, the tool 36comprises a cylinder-like wall 36, an annular radial flange 38 connectedto a bottom of the conical wall 36 and seated on the base 12, and ahorizontal member 40 disposed inside and connected to the cylinder-likewall 36 near the top of the latter. Respective surfaces of the top seal14, sleeve 16, cylinder-like wall 36, and annular radial flange 38define a ring-shaped cure volume 8. The top of the cylinder-like wall 36abuts the top plate 14 with a pair of seals 28 therebetween. The bottomof sleeve 16 abuts the annular radial flange 38 of tool 34 with a seal28 therebetween. An appropriate interface between the heating elementsintegrated in the tool 34 and the source of energy (e.g., heated fluidor electric current) can be provided in the base 12, the interfaceelements being aligned by manipulation of tool 34 as it is lowered ontothe base 12.

The horizontal member 40 may be designed to withstand the cure pressurein ring-shaped cure volume 8. For example, horizontal member 40 maycomprise a plate with supporting structure as required to react pressureloads. In accordance with an alternative implementation, the annularradial flange 38 and horizontal member of tool 34 could be eliminated ifthe cylinder-like wall 36 were designed to react pressure loads, with orwithout reaction of pressure loads by top plate 14 and base 12. In thiscase the top and bottom of the cylinder-like wall 36 of tool 34 will berespectively sealed to top plate 14 and base 12.

The apparatus depicted in FIG. 2 is assembled by first placing anuncured composite structure 22 in contact with a surface of a tool 20having a closed contour and having integrated heating elements, theresult being a tool-composite structure assembly. That tool-compositestructure assembly is then placed on a base 12. FIG. 6 is a blockdiagram showing some components and subsystems of a system forassembling the apparatus depicted in FIG. 2. The tool 20 (with theuncured composite structure supported thereon) is manipulated (indicatedby a downward arrow in FIG. 6) into proper position (using indexing)onto the base 12 by tool handling equipment 44. When the tool 20 ispositioned correctly, the heating elements integrated in the tool 20will be coupled to a source of energy via the manifold 24 seen in FIG.2. After the heating elements have been successfully coupled, the topplate 12, with sleeve 18 and plug 16 attached or connected thereto, islowered (indicated by a downward arrow in FIG. 6) into position usinglifting equipment 42. More specifically, the rigid structure formed bytop plate 14, sleeve 16 and plug 18 is lowered until the bottom edges ofsleeve 16 and plug 18 abut and are sealed against the upper surface ofbase 12, as seen in FIG. 2. Optionally, the bottom edges of sleeve 16and plug 18 are inserted into recesses formed in base 12, as depicted inFIG. 3A.

Upon completion of the assembly of the apparatus depicted in FIG. 2, anairtight ring-shaped cure volume 8 is formed. The temperature andpressure inside the cure volume are then controlled in accordance withthe cure cycle specified for the particular uncured composite structurebeing cured. As depicted in FIG. 7, the heating elements 52 inside thecure volume 8 are activated by a temperature control system 46 while aspecified pressure is produced inside the cure volume 8 by a pump 54operated by a pressure control system 48. The heating elements 52includes at least a plurality of heating elements integrated in thetool, which heat the uncured composite structure by thermal conductionand/or radiation, and optionally also includes heaters 30 and 32 seen inFIG. 4, which heat the atmosphere inside the cure volume 8.

After the cure cycle has been completed, the heating elements 52 andpump 54 are turned off and the cured composite structure is allowed tocool. The top plate 14 and associated walls are raised by the liftingequipment 42 (see FIG. 6); then the tool 20 (with the cured compositestructure supported thereon) is raised and separated from the base 12using the tool handling equipment 44; and then the cured compositestructure is demolded from the tool 20.

The curing apparatus and methodology disclosed herein has the followingtechnical advantages:

(1) A typical cure vessel (autoclave) must be significantly larger thanthe part/tool, and is usually sized to accommodate curing of multipleparts (batch processing). Thus the energy and inerting required toachieve the necessary cure pressure profiles and inert environment issignificant. The apparatus disclosed herein only involves pressurizationand inerting of a volume that is only nominally larger than thepart/tool.

(2) The mode of heat transfer in an autoclave or oven to heat thetool/part is primarily convection, which is inefficient, and consistentair velocities which are essential for uniform curing are difficult toachieve, especially when multiple parts are cured simultaneously. Theapparatus disclosed herein provides heat via thermal conduction and/orradiation using integrally heated tools, supplemented as required byother heating methods such as infrared heaters (radiation). This enablesincreased temperature and pressure ramp rates, and thus reduces energyconsumption and fabrication cycle time.

(3) Given their size and complexity, the cost and lead time to procureautoclaves is much higher than the smaller cure apparatus disclosedherein.

(4) The methodology disclosed herein involves an approach to compositepart cure that is “right-sized” to the part and supports leanmanufacturing objectives.

(5) With a typical autoclave, achieving current maximum cure temperatureramp rates (e.g., 5° F./minute) can be unachievable for larger or morecomplicated nacelle composite parts. The apparatus and methodologydisclosed herein not only make that possible, but also enable far morerapid and uniform heating rates, thus significantly reducing cure cycletime without degradation of part quality.

The apparatus and methodology disclosed herein have significantpotential for reduced capital cost and lead time, reduced partfabrication cost and lead time, and reduced energy consumption.

The apparatus and method disclosed above may be employed in an aircraftmanufacturing and service method 200 as shown in FIG. 8 formanufacturing and servicing an aircraft 202 as shown in FIG. 9. Duringpre-production, exemplary method 200 may include specification anddesign 204 of the aircraft 202 and material procurement 206. Duringproduction, component and subassembly manufacturing 208 and systemintegration 210 of the aircraft 202 take place. Thereafter, the aircraft202 may go through certification and delivery 212 in order to be placedin service 214. While in service by a customer, the aircraft 202 isscheduled for routine maintenance and service 216 (which may alsoinclude modification, reconfiguration, refurbishment, and so on).

Each of the processes of method 200 may be performed or carried out by asystem integrator, a third party, and/or an operator (e.g., a customer).For the purposes of this description, a system integrator may includewithout limitation any number of aircraft manufacturers and major-systemsubcontractors; a third party may include without limitation any numberof venders, subcontractors, and suppliers; and an operator may be anairline, leasing company, military entity, service organization, and soon.

As shown in FIG. 9, the aircraft 202 produced by exemplary method 200may include an airframe 218 with a plurality of systems 220 and aninterior 222. Examples of high-level systems 220 include one or more ofthe following: a propulsion system 224 (including engine nacelles of thetype described above), an electrical system 226, a hydraulic system 228,and an environmental control system 230. Any number of other systems maybe included. Although an aerospace example is shown, the principlesdisclosed herein may be applied to other industries, such as theautomotive industry.

The apparatus and methods embodied herein may be employed during one ofthe stages of the production and service method 200. For example,composite nacelle components or subassemblies fabricated or assembledduring component and subassembly manufacturing 208 may be cured usingthe apparatus and methods disclosed herein, thereby reducing themanufacturing cost of an aircraft 202.

While apparatus and methods for have been described with reference tovarious embodiments, it will be understood by those skilled in the artthat various changes may be made and equivalents may be substituted forelements thereof without departing from the teachings herein. Inaddition, many modifications may be made to adapt the concepts andreductions to practice disclosed herein to a particular situation.Accordingly, it is intended that the subject matter covered by theclaims not be limited to the disclosed embodiments.

The method claims set forth hereinafter should not be construed torequire that the steps recited therein be performed in alphabeticalorder (any alphabetical ordering in the claims is used solely for thepurpose of referencing previously recited steps) or in the order inwhich they are recited. Nor should they be construed to excluderespective portions of two or more steps being performed concurrently oralternatingly.

The alternative structures corresponding to the “a means forpartitioning” recited in the claims include at least the following: plug18 depicted in FIG. 1 and equivalents thereof; and tool 36 depicted inFIG. 5 and equivalents thereof. The alternative structures correspondingto the “means for producing a specified pressure” recited in the claimsinclude at least the following: pump 54 depicted in FIG. 1 andequivalents thereof.

The invention claimed is:
 1. An apparatus for curing a composite structure, comprising: an enclosure comprising a top plate, a base, and an outer wall disposed between said top plate and said base, said outer wall having a closed contour; an inner wall disposed between said top plate and said base and surrounded by said outer wall, said inner wall having a closed contour, wherein surfaces of said inner and outer walls, said top plate, and said base define a ring-shaped cure volume; and a hollow tool made of metal or composite material, said hollow tool comprising a surface having a closed contour and embedded heating elements, wherein said hollow tool surrounds said inner wall and is surrounded by said outer wall.
 2. The apparatus as recited in claim 1, wherein said heating elements carry heated fluid.
 3. The apparatus as recited in claim 1, further comprising a heater attached to an outer surface of said inner wall.
 4. The apparatus as recited in claim 1, further comprising a heater attached to an inner surface of said outer wall.
 5. The apparatus as recited in claim 1, wherein said inner and outer walls are supported by and extend from said top plate to form a unit that is separable from said base.
 6. The apparatus as recited in claim 1, further comprising a first seal disposed between said inner wall and said base and a second seal disposed between said outer wall and said base.
 7. The apparatus as recited in claim 6, wherein said base comprises first and second recesses in which said first and second seals are respectively seated.
 8. An apparatus for curing a composite structure, comprising: an enclosure comprising a top plate, a base, and a wall disposed between said top plate and said base, said wall having a closed contour and; a hollow tool made of metal or composite material, said hollow tool being disposed between said top plate and said base and surrounded by said wall, said hollow tool comprising a surface having a closed contour and embedded heating elements, wherein said surface of said hollow tool and respective surfaces of said wall and said top plate at least partly define a ring-shaped cure volume.
 9. The apparatus as recited in claim 8, wherein said cure volume is further partly defined by a surface of said base.
 10. The apparatus as recited in claim 8, further comprising means for coupling said heating elements in said tool to a source of energy.
 11. The apparatus as recited in claim 10, wherein said heating elements transform electric current into heat and said source of energy is a current generator electrically coupled to said heating elements.
 12. The apparatus as recited in claim 10, wherein said heating elements carry heated fluid and said source of energy is a source of heated fluid.
 13. The apparatus as recited in claim 8, further comprising a heater attached to an inner surface of said wall.
 14. A system comprising: an enclosure comprising a top plate, a base, and an outer wall disposed between said top plate and said base, said outer wall having a closed contour that forms an outer boundary of an internal volume of said enclosure; a hollow tool for partitioning said internal volume of said enclosure to form a ring-shaped cure volume disposed between said wall and said hollow tool, said hollow tool being made of metal or composite material; an uncured composite structure disposed within said ring-shaped cure volume, said uncured composite structure being in contact with a surface of the hollow tool and not in contact with the outer wall; heating elements embedded in said hollow tool for heating said uncured composite structure by heat transfer during a cure cycle; and means for producing a specified pressure inside said ring-shaped cure volume during the cure cycle.
 15. The system as recited in claim 14, wherein said hollow tool comprises a surface having a closed contour, said heating elements being integrated in said tool, and said surface of said tool being surrounded by said outer wall and thermally coupled to the uncured composite structure to allow heat transfer from said heating elements to the uncured composite structure.
 16. A system comprising: an enclosure comprising a top plate, a base, and an outer wall disposed between said top plate and said base, said outer wall having a closed contour that forms an outer boundary of an internal volume of said enclosure; an inner wall for partitioning said internal volume of said enclosure to form a ring-shaped cure volume disposed between said inner and outer walls; a hollow tool made of metal or composite material, said tool comprising a surface having a closed contour, said surface of said hollow tool surrounding said inner wall and being surrounded by said outer wall; an uncured composite structure disposed within said ring-shaped cure volume, said uncured composite structure being in contact with the surface of the hollow tool and not in contact with the outer wall; heating elements embedded in said hollow tool for heating said uncured composite structure by heat transfer during a cure cycle; and means for producing a specified pressure inside said ring-shaped cure volume during the cure cycle.
 17. The apparatus as recited in claim 1, further comprising an uncured composite structure that is in contact with the surface of the hollow tool and not in contact with the outer wall.
 18. The apparatus as recited in claim 8, further comprising an uncured composite structure that is in contact with the surface of the tool and not in contact with the wall. 